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BURBAGE VALLEY,
DERBYSHIRE |
| Burbage
valley is 8km north-west of Sheffield. The valley is
drained by Burbage brook, a tributary of the R. Derwent.
The valley has been carved through two different types of
rock - 'millstone grit' and 'shale'. Within this small
area we can explore the range of factors which affect the
work of rivers. |
 1.
Burbage brook rises on a
moorland plateau. Beneath the surface are impermeable gritstone rocks, so this moorland is very wet.
The poor drainage means that vegetation does not rot
easily, and a layer of peat has formed over the surface.
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2.
In the upper valley the concave slopes
are formed with millstone grit at the top and shale beneath. Around the 'rim' of the valley is a
crag of millstone grit known locally as an 'edge'.
Millstone grit is a resistant rock which has distinctive bedding and jointing planes. Frost shattering in the 'ice age' expanded these cracks and
divided the rock into blocks. Some of the blocks of
weathered rock have tumbled from the crags, and rolled or
slid down the slopes. This is called mass movement.
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 3.
In most of the valley Shale is the rock which
forms the valley floor. It is a soft rock, with numerous
thin beds. It is easily broken by weathering and easily eroded by the river. It is
impermeable and the
waterlogged beds of shale are likely to cause landslides.
In this view we see the orange colouring in the water
which tells us that the shale is being chemically
weathered, and the iron compounds are being washed into
the river.
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 4.
In the upper part of the
valley the river flows over resistant beds of gritstone,
The bed of the stream is steep, making it fast-flowing.
The energy of the fast flowing water allows it to
transport large boulders (in times of flood) as 'bedload'. At this point
the valley sides are steep and the floor of the valley is
narrow. Boulders are tumbled down the steep sides of the
valley by Mass Movement.
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5.
In the central part of
the valley, the width increases. The valley 'opens out'.
The skyline is still dominated by gritstone capped hills.
The shale beneath has been smoothed and the angle of the
valley sides reduced. Coniferous woodland has been
planted in this part of the valley. Elsewhere the rough
grazing, of coarse grass and bracken, is food for a few
sheep. This area is not economically favourable for
farming.
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6.
In the middle section of the valley the river meanders. At the outside of the bends the
river undercuts the hillside and landslides
occur(see below), bringing rock and soil debris into the
river. At the inside of the bend is a flatter area, built
up over time by deposition.
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7.
Here we see how open the middle section of the valley
has become. In the distance the plateau
of Burbage Edge is fringed with cliffs, formed of
resistant millsone grit. The slopes beneath the 'edges'
are littered with gritstone blocks which are being
carried downhill by mass movement.
Weathered shale has been formed into soil, which has
become vegetated. Close to the river are steeper slopes
created by landslides.
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8.
The flat topped hill called Higger Tor
lies to the west of the valley. Notice the difference in
slope angle between the resistant gritstone and the less
resistant shale. Notice also the rough vegetation which
grows on the poor badly drained soils.
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9.
This is 'Toads Mouth bridge' which carries the main
road across Burbage brook. Downstream from the bridge the
valley opens out even more.
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 10.
In the lower section of the valley the river is wider,
and contains more water. The gradient of the bed is
gentler. The valley sides are gentler. Soils are deeper
and better developed so the grass is better. Mixed
woodland is the natural vegetation of this area.
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